1. Field of the Invention
The present invention relates generally to a portable terminal having a tuner, and in particular, to a portable terminal having a tuner for changing an antenna radiation pattern by changing the current distribution of a ground provided to the portable terminal.
2. Description of the Related Art
As portable terminals are equipped with a variety of functions owing to the development of information communication technology, the trend for providing terminals of smaller size, of lighter weight and of improved portability. In an initial developmental stage where wireless communication is deployed, the portable terminals were confined to voice call, short message transmission, and the like, whereas they are becoming capable of transmitting/receiving multimedia data such as moving pictures provided by service providers, video conferencing via a wireless Internet, and moving picture mail.
A portable terminal is a unit that allows a user to wirelessly communicate with another party. Portable terminals include HHP (Hand Held Products), CT-2 (Cordless Telephone-2) cellular phones, smart phones, digital phones, PCS (Personal Communication Service) phones, PDAs (Personal Digital Assistants), and laptop computers, typically categorized according to their appearance.
The portable terminals usually use an LCD (Liquid Crystal Display) as a data output device. A keypad, a basic data input device, is provided via an arrangement of keys.
An antenna device is positioned appropriately for receiving a signal. Providing increased efficiency and, as more recently has become an issue, reduced SAR (Specific Absorption Rate) are challenging issues in designing the antenna device.
For applications to conventional portable terminals, whip antenna, helical antenna, sleeve antenna, N-type antenna, chip antenna, and FS-PIFA antenna are provided at the outside of the portable terminal. Thus, these antennas are called external antennas. On the other hand, inverted F antenna, planar inverted F antenna (PIFA), diversity antenna, microstrip antenna, twisted loop antenna, and EID (Electronic Identification) antenna are internal antennas that can be installed within the portable terminals.
Antennas utilized in portable terminals can also be divided into monopole or planar types according to how they excite radiated electromagnetic waves. Monopole type antennas include whip antenna, helical antenna, sleeve antenna, chip antenna, and N-type antenna, while planar type antennas include inverted F antenna, PIFA, diversity antenna, microstrip antenna, EID antenna, FS (FireStick)-PIFA, and RCDLA (Radiation Coupled Dual L-Antenna).
Although they typically operate in wide bands, the monopole antennas can create strong electromagnetic waves that have been alleged to adversely affect the human body. While it is easy to suppress the effects of electromagnetic waves from the planar antennas, these antennas do not have wide bands.
While the monopole antennas are external ones, recently developed antennas include a half-exposed, fixed monopole antenna, an internal monopole antenna with an electromagnetic wave absorber, as well as a SAR-reducing monopole antenna for a folder-type terminal, which have internal structures, operate in wide bands, and provides a low SAR.
The half-exposed, fixed monopole antenna provide excellent antenna efficiency, but is not as effective in reducing SAR as the wave absorbing internal monopole antenna. To the contrary, although the wave absorbing internal monopole antenna reduces SAR more effectively than the half-exposed, fixed monopole antenna, it has lower antenna efficiency.
As with a typical whip antenna, impedance matching is difficult due to the increase of coupling between an antenna element and the folder of a terminal in the half-exposed, fixed monopole antenna. Also, close arrangement of the antenna element and other terminal components decreases radiation efficiency. The requirement for a predetermined ground area makes it difficult to make the terminal thinner.
The monopole antenna designed for SAR reduction in a folder-type terminal, which was proposed to overcome the above problems, is excellent in both antenna efficiency and SAR reduction.
In the monopole antenna, however, because an electromagnetic wave absorber is positioned in the vicinity of a hinge device that connects two terminal bodies, electromagnetic wave leakage in the hinge device may lead to a SAR increase.
As illustrated in FIG. 1, FIG. 2 and FIG. 3, a folder-type portable terminal comprises a main body 10 having a plurality of keys 11 which are pressed to enter intended data and a microphone 12, a folder 20 having a main LCD 21, a sub LCD 24 for displaying input data, a speaker 22, a PCB 23 in the folder 20 and a hinge device 30 which connects the body 10 and the folder 20 along a hinge axis A1 and is rotatable so that the folder 20 advances toward or recedes away from the body 10.
Traditionally, the width of the folder 20 is relatively made wide as compared to its length, or the hinge axis A1 is defined near an antenna device 40 on the main body 10, for sake of fabrication convenience.
Therefore, electromagnetic waves from a power supply for the antenna can leak in the hinge device 30, which is positioned between the main body 10 and the folder 20, thereby increasing SAR.
Moreover, if the antenna is a monopole antenna, a ground surface perpendicular to an antenna element is needed within an upper portion of the main body 10. However, due to the hinge device 30, a sufficient antenna ground area is difficult to ensure and reduction of the thickness of the portable terminal is limited.
Meanwhile, a SAR-reducing folder-type terminal has been developed. It has the same configuration as the conventional folder-type portable terminal, except that an electromagnetic wave reflecting plate is attached on the inner or outer surface of the folder 20 such that it faces the antenna device when the folder 20 is opened.
In this case, the antenna can be a helical antenna, a whip antenna, or a half-exposed, fixed monopole antenna. Use the half-exposed, fixed monopole antenna, allows the antenna ground surface to be easily obtained by the reflecting plate. If the antenna ground surface must be secured on the upper surface of the main body by using the whip or helical antenna, the ground surface itself will be narrow.
Folder-type portable terminals typically have a ground larger than ¼λ of its operating frequency, e.g. 1800 MHz. The ground refers to a part of the main body or folder where electrical current flows. Depending upon the current distribution of the folder, a radiation pattern can greatly vary. Because there is no specific solution for SAR reduction, SAR, reduction, attempts have been made to reduce SAR by lowering antenna output, thereby deteriorating the operation characteristics of the antenna device.
The radiation pattern of the existing folder-type portable terminal depends predominantly on a limited ground size of the terminal. The radiation pattern of the portable terminal affects SAR as well as the operation performance of the terminal. Conventional SAR reduction techniques are accompanied by degraded antenna radiation performance, which in turn degrades the operation performance of the portable terminal.